This invention is generally in the field of bio-molecular electronics, and relates to electrical devices with biological components.
The following publications are believed to be relevant to the Background section of the specification.
1. Fromherz, P., xe2x80x9cInterfacing Neurons and Silicon by Electrical Inductionxe2x80x9d, Ber. Bunsenges. Phys. Chem., 100:1093-1102 (1996).
2. Stett, A., Mÿller, B., Fromherz, P., xe2x80x9cTwo-way Neuron-Silicon Interface by Electrical Inductionxe2x80x9d, xe2x80x9cPhys. Rev. B., 55:1779-1781 (1997).
3. Offenhaussser, A., et. al., xe2x80x9cNeuronal Cells Cultured on Modified Microelectronic Device Surfacesxe2x80x9d, J. Vac. Soc. Technol. A., 13(5):2606-2612 (1995).
4. Potomber, R. S., Matsuzawa, M., Leisi, P., xe2x80x9cConducting Networks from Cultured Cells on Self-assembled Monolayersxe2x80x9d, Synthetic Metalsxe2x80x9d, 71, 1997 (1995).
5. Stett, A., Mÿller, B., Fromherz, P., xe2x80x9cTwo-way Neuron-Silicon Interface by Electrical Inductionxe2x80x9d, xe2x80x9cPhys. Rev. B., 55:1779-1781 (1997).
6. Matsuzawa, M., Umemura, K., Beyer, D., Sugioka, K., Knoll, W., xe2x80x9cMicropatterning of Neurons using Organic Substances in Culturexe2x80x9d, Thin Solid Films, 305:74-79 (1997).
7. Dulcey, C. S., Georger, J. H., Krauthamer, V., Stenger, D. A., Fare, T. L., Calvert, J. M., Science, 252:551 (1991).
8. (a) Cohen, R., Zenou, N., Cahen, D., Yitchaik, S., xe2x80x9cMolecular Electronic Tuning of Si Surfacesxe2x80x9d Chem. Phys. Lett., 279:270-274 (1997);
(b) Zenou, N., Zelichenok, A., Yitzchaik, S., Cohen, R., Cahen, D., xe2x80x9cTuning the electronic properties of silicon via molecular self-assemblyxe2x80x9d in xe2x80x9cThin Organic Filmsxe2x80x9d, C. W. Frankxe2x80x94Ed, ACS Symp. Ser., 695:57-66 (1998).
9. Yitzchaik, S., Marks, T. J., xe2x80x9cChromophoric Self-Assembled Superlatticesxe2x80x9d, Acc. Chem. Res., 29:197-202 (1996) and references therein.
10. 08/857,769 of May 1997.
11. U.S. Pat. No. 5,156,918.
12. Surplice, N. A.; D""Archy, R. J. J. Phys. E: Sc. Instr. 1970, 3, 477-482.
Interaction between neurons and electronic devices have been in existence for several decades for a plurality of purposes. During the past decades, these interactions were usually achieved by inserting an electrode or an array of electrodes into the neurons or placing an electrode or an array of electrodes in the vicinity of the neurons"" membranes so as to detect voltage changes. The detection electrode or array of electrodes can also be used for the stimulation of neurons.
With the growing body of knowledge concerning transistors and semi-conductors there have been several attempts directed at the coupling the two types of information flow: electron conduction in solids (achieved by the transistor), and ion conduction in aqueous environments (carried out by the neurons). However, the coupling between the transistors and the neurons suffered from a series of problems including basic scientific problems as well as technological difficulties. Direct coupling of neurons to enhancement type MOS transistors requires the application of a DC bias between the biological solution and the transistor substrate in order to create a conducting channel. The combination of the DC bias, the biological ionic solution and the transistor, is a potential source for a series of degradation processes resulting from leakage currents, heat generation, electrochemical corrosion and ionic drift instabilities. All this will eventually lead to damage of the neuron and/or the transistor.
The publication of Stett et al. (Ref. 2) describes a nerve cell which is placed on a combined microstructure of an insulated spot of doped silicon and an insulated-gate field effect transistor. The neuron was placed on the transistor without any adhesive material. Voltage pulses are applied by the insulated spot to the neuron through capacitive coupling. They elicit neuronal activity which in turn can be detected by the transistor. The article describes a bi-directional interface between the ionics of the neuron and the electronics of the silicon, achieved by two separate modalities. Here, however two separate locations on the silicon chip spaced-apart in a horizontal plane are used, namely, one for sensing of neuronal activity achieved by an insulated-gate field effect transistor, and the other for capacitive simulation of neuron activity achieved by an insulated spot of doped silicon. This approach of two separate locations, one for the neuron activation and one for sensing its activity, imposes several limitations in multi neuron multi transistor systems, as follows:
it requires accurate positioning of each neuron on the electronic circuit;
it increases the number of electronic connections to a given neuron system; and
it requires larger area of the electronic system.
It is highly desirable to provide coupling between neurons, (and other voltage sensitive cells) and electrical devices both for the purpose of detecting electrical activity in these cells, and for stimulating the cells via said electrical devices. The coupling should be such which allows the detection and stimulation by use of a relatively simple electronic structure, and in addition, the electrical structure should be bio-compatible and the mode of its coupling should be such as not to produce the electrochemical changes and toxic substances which are harmful to live cells.
The term xe2x80x9cchemical synapsesxe2x80x9d, refers to a junction between two neurons wherein the axon terminals of a pre-synaptic cell, containing a vesicle filled with a particular neurotransmitter substance, are in close vicinity to the membranes of a post synaptic cell. When the nerve impulse reaches the axon terminal the vesicles are exocytosed releasing their neurotransmitter components into the synaptic cleft which is the narrow space between the pre-synaptic and the post synaptic cell. The transmitter diffuses across the synaptic cleft, and then binds to receptors on the post synaptic cells. Upon binding, the neurontransmitter induces a change in the ionic permeability of the post synaptic membrane that results in the disturbance of the electrical potential at this point. If the electrical disturbance is sufficiently high it can induce an action potential, or a muscle contraction (where the cell is a muscle), or alternatively, may be sufficient to trigger release of hormones from gland cells.
Although the chemical synapse site is a major component in the modulation of neuronal activity, said modulation effecting properties such as memory, learning, degradation due to various neurodegenerative diseases, the physiological phenomena of the synapse was studied and utilized mainly in biological systems.
Possible means for communication between nerve cells and transistors may be polarizable molecules. Such molecules are described in Ref. 9. Furthermore, U.S. patent application Ser. No. 08/857,769, May 1997, and U.S. Pat. No. 5,156,918 concern methods for forming a polymeric structure composed of two or more discrete monolayers wherein at least one layer is composed of polycyclic aromatic molecules with a defined Z-axis oriented substantially normal to the plane or at an angle close to normal, up to ca. 45xc2x0. Ref. 8 further addresses the effects of polarizable molecules on the electronic properties of silicon.
Glossary
xe2x80x9cVoltage sensitive cell (VSC)xe2x80x9dxe2x80x94a cell in which normal physiological activity is modulated by voltage changes across its membrane. Typical examples are neurons, muscle cells and cells of glands which secrete hormones as a result of voltage change.
xe2x80x9cElectrical junctionxe2x80x9dxe2x80x94a functional connection between a single transistor and at least one VSC enabling signal transfer in at least one direction, either from the transistor to the VSC, or from the VSC to the transistor through capacitive coupling.
xe2x80x9cDC biasxe2x80x9dxe2x80x94the voltage applied between the biological solution in which the VSC is embedded and the transistor substrate, which sets the transistor ready for sensing the VSC activity (i.e., xe2x80x9copensxe2x80x9d the transistor).
xe2x80x9cExternal surface of the transistorxe2x80x9dxe2x80x94the outer surface of an uppermost, insulating layer covering the active component of the transistor.
xe2x80x9cBinding moietiesxe2x80x9dxe2x80x94refers to molecules which may be of a biological or non-biological origin which can bind to components present on the membrane of the VSC. By a preferred embodiment, the moieties form together with components present on the membrane of the VSC, xe2x80x9ca specific pair-forming groupxe2x80x9d (see below). For example, where the membranal component is an antigenic epitope, the binding moiety is an antibody, where the membranal component is a receptor, the binding moiety is its specific ligand, or an adhesion moiety capable of xe2x80x9caffinity bindingxe2x80x9d (see below) thereto, where the membranal component is a glycoprotein, the binding moiety is a lectin, etc. By other embodiments, the binding of the binding moieties to the membranal component is by non-affinity bindings such as by hydrophobic interactions due to hydrogen bonds or due to van der-Wallace interactions. It should be noted that this term does not necessarily refer to the full molecule which interacts with the VSCs membranal component, and may only refer to the region of the full molecule which binds to said membranal component. For example, where the membranal component is a receptor, the binding moiety may be only a sequence of the adhesion molecule which specifically binds to said receptor.
xe2x80x9cA specific pair forming groupxe2x80x9dxe2x80x94two biological molecules which are capable of affinity binding (see below) to each other. Each member of the group is capable of identifying and interacting with its specific counter partner form among similar molecules of other species. For example, if a pair forming group is an antibody and its specific antigen, then the antibody is capable of specifically discriminating and interacting with the specific antigen, while not interacting with similar antigens present in the environment.
xe2x80x9cAffinity bindingxe2x80x9dxe2x80x94refers to the specific non-covalent interaction between two members of a specific pair forming group.
xe2x80x9cHyper-polarizable chromophoresxe2x80x9dxe2x80x94are typically aromatic molecules characterized in that that they contain an electron donating moiety, an electron withdrawing moiety separated by a xcfx80-bridge. The family includes also chromophores with high field polarization properties, i.e. nth order hyper-polarizable chromophores. They are sometimes referred to as voltage sensitive dyes which have a positively charged chromophore and a negatively charged counter-ion which is ionically bound to the chromophore. The classical voltage-sensitive dye respond to voltage pulses by electrochromism, i.e. upon excitation, the molecules undergoes a shift of the positive pole. In a hyper-polyrizable chromophore, an electrical excitation from an action potential of a nerve cell modulates the distribution of the xcfx80-electrons, i.e. the charge distribution along the molecule which leads to a large change in the dipole moment of the molecule. Both, the anion flipping and the change in the dipole moment effect the transistor to which these hyper-polarizable chromophores are attached.
xe2x80x9cFloating gatexe2x80x9dxe2x80x94an insulated electrode of a MOS transistor on which an electric field is applied, thereby inducing an electric field to the active component of the transistor through capacitive coupling.
xe2x80x9cDepletion type devicexe2x80x9dxe2x80x94an insulated-gate field-effect transistor in which free carriers are present in the channel (active component) when the gate-source voltage is zero. Channel conductivity thus exists at zero voltage between gate and source and is controlled by changing the magnitude and polarity of the gate voltage. A depletion type device is normally-on. For the normally-on depletion device, a current can flow at a zero gate potential, and the current can be increased or decreased by varying the gate voltage.
xe2x80x9cSpacerxe2x80x9dxe2x80x94A molecule or group of molecules used to bridge the gap between the surface of the transistor and the VSC so as to minimize the xe2x80x9cshuntxe2x80x9d caused by the electrolyte containing solution. The spacers of the present invention may be attached to hyper-polarized chromophores so as to bridge the varying distances between the surface of the transistor and the VSC so that when the electrical junction is formed, the space between the surface of the transistor and the uneven surface of the membrane of the VSC is bridged by the spacer and the conjugated hyper-polarizable chromophore, notwithstanding the fact that the membrane itself is uneven so that the spacer has varying dimensions at different regions. The spacers may also be used to place the binding moieties at varying distances from the transistor surface so that the binding moiety may bind to membranal components on the VSC notwithstanding that its components are at varying distances from the surface of the transistor.
By another alternative, the spacer may be used by itself so as to simply xe2x80x9cclosexe2x80x9d the gap between the surface of the transistor and the VSC so as to minimize the shunt. Typically, the length of the spacer ranges from 1 nm to 30 nm. Typically the spacer should be any inert molecule such as oligosaccharides, straight hydrocarbons, branched hydrocarbons, peptides, etc. A spacer may also be a combination of one of the above-mentioned inert molecules bound to a hyper-polarizable molecule. Alternatively, the spacer may be made of multi-layers of chromophores or dendritic structures of chromophores, thus the spacer is an xe2x80x9cactivexe2x80x9d component.
xe2x80x9cAgent secreting cellxe2x80x9dxe2x80x94a cell which normal biological, activity is secretion of agents to the extracellular environment. Examples of agent secreting cells are neurons which secrete neurotransmitters, gland cells which secrete hormones and the like.
xe2x80x9cAgent secreting region of the cellxe2x80x9dxe2x80x94the region of the agent secreting cells from which the agent is secreted. Where the agent secreting cell is a neuron, this region is the pre-synaptic region.
xe2x80x9cElectrochemical junctionxe2x80x9dxe2x80x94refers to a functional connection between an agent secreting cell and a transistor. The agent secreting cell should be positioned in such an orientation so that the agent secreted therefrom can reach the transistor. While by one embodiment the orientation may be adjacent positioning, such as in a chemical synapse where the cells and the transistor are adjacent, by other embodiments the orientation may be non-adjacent, for example, if the transistor is placed inside a body, and the blood circulation may bring agent secreted from the agent secreting cell present at a distanced location to the transistor. The transistor has immobilized thereon recognition moieties which are capable of affinity binding to the secreted agent. The affinity binding between the recognition moiety and the agent causes a change of at least one electrochemical property of the transistor such as capacitance.
xe2x80x9cRecognition moietiesxe2x80x9dxe2x80x94biological molecules capable of forming a specific pair forming group with the secreted agent. Typically, where the secreted agent is a neurotransmitter or a hormone, the recognition moieties are the receptors for the neurotransmitter or the hormone, respectively.
xe2x80x9cCatalytic moietiesxe2x80x9dxe2x80x94molecules having an activity which discontinue the affinity binding between the recognition molecule and the agent, for example, by degradation of the agent.
By one of its aspects, the present invention concerns an electrical junction between a single transistor and at least one voltage sensitive cell (VSC). The electrical junction of the invention typically shows at least one of the following advantageous characteristics:
It enables bi-directional voltage transfer between the transistor and the VSC. This means, that by utilization of a single transistor, it is possible both to detect voltage changes from the VSC (for example to detect neuronal activity in neurons) and using the same modality also to stimulate the VSC by capacitance changes of voltage. In this case, the transistor is a floating gate depletion type device, and the VSC is associated with the floating gate and is capable of being stimulated by a voltage pulse applied to the source, channel and drain of the transistor.
When using the transistor in the form of a depletion type device in the junction of the present invention, it can also be characterized in that it does not need a DC bias to be applied between the transistor and the solution containing the VSC. This means, that the VSC is not under a constant stimulation by a DC voltage application. Typically, living cells deteriorate after a prolong application of voltage to their members, and thus an electrical junction without a DC voltage bias enables to maintain the VSC in a viable form for prolonged periods of time.
The omission of the DC bias means also that there is significantly less risk for electrochemical corrosion of the transistor through reaction with the ionic biological solution.
By another characterizing property the electrical junction of the invention enables the anchoring of the VSC to the external surface of the transistor by binding moieties, which are conjugated at one end to the external surface of the transistor, and at the other end are capable of affinity binding with membranal component on the VSC membrane. These binding moieties significantly decrease the size of the cleft between the membrane of the VSC and the external surface of the transistor, thus minimizing the xe2x80x9cshuntxe2x80x9d of the electrical caused by the aqueous solution present in said cleft. Optionally, the closure of the xe2x80x9cshuntxe2x80x9d may be improved by use of spacers.
Another possible characterizing feature of the electrical junction of the invention is that the voltage transfer between the membrane of the VSC and the external surface of the transistor, in both directions, is mediated by hyper-polarizable chromophore.
Thus, the present invention concerns an electrical junction between one transistor and at least one voltage-sensitive cell (VSC) characterized by at least one of the features selected from the group consisting of:
(i) voltage transfer between the transistor and the VSC is bi-directional, the transistor being a floating gate depletion type device, the VSC being associated with the floating gate and being capable of being stimulated by a voltage pulse applied to the source, channel and drain of the transistor;
(ii) there is no DC bias between the transistor and the solution containing the VSC, the transistor being a depletion type device;
(iii) the VSC is anchored to the external surface of the transistor by binding moieties, optionally through spacers;
(iv) the voltage transfer between the membrane of the VSC and the external surface of the transistor, and between the external surface of the transistor and the membrane of the VSC is mediated by a hyper-polarizable chromophore;
(v) a combination of two or more of the features of (i) to (iv).
The electrical junction of the invention enables through formation of a transistor neuron hybrid the coupling between electrical devices and voltage sensitive cells (neurons, muscle cells and gland cells) for various utilities as follows:
(1) It may be used as an in vivo sensor in order to detect electrical activity in voltage sensitive cells, (such as neurons);
(2) It may be used in vivo in order to stimulate nerve cells or muscle cells, for example for stimulation of muscle cells of paralyzed limbs in order to achieve some sort of movement of the muscles even if they do not receive neuronal input from motor neurons;
(3) It may be used both for detection of neuronal pulses and stimulate of voltage sensitive cells. For example where a neuron or muscle activated prosthesis is used. In such a case, it is necessary to stimulate nerve cells or the muscle cells in order to produce movement in the prosthesis. And in addition it may be desirable to record from other nerve cells or muscle cells in order to receive a feedback information concerning the position, and movement thereof in order to enable coordinated movements and correction of mistakes and this enabling smooth movement of the prosthesis.
(4) The transistor-neuron hybrid may be used in various artificial sensing devices, such as devices which have an ability to sense light (xe2x80x9cartificial eyexe2x80x9d) or sound (xe2x80x9cartificial earxe2x80x9d). This will enable to activate regions of the central nervous system connected to sight or hearing by stimulating these regions with light or sound input obtained from electrical devices (such as a camera or a microphone) so as to enable processing of the artificially produced information by the central nervous system. The transistor-neuron hybrid may be used to record impulses from sensing organs themselves (the eye or the ear) and transfer the electrical output to electrical devices, such as computers, capable of processing the information, for example, in cases where the sensing organ (eye) is functional but the visual cortex region which should have processed the visual information is impaired.
(5) By another option, the transistor-neuron hybrid will enable the creation of a xe2x80x9cbrain-computerxe2x80x9d hybrid structure which will enable new breakthroughs in calculation and intelligence processing using both the computational power of an electrical computer and the flexibility and adjustability properties of a biological central nervous system.
As indicated above, the bi-directional voltage transfer between the VSC and the transistor is achieved by the use of a depletion type transistor with floating gate for both the neuron sensing and stimulation purposes. The depletion type doping level is such that the application of voltage required for the stimulation of the VSC, will not deplete the channel. This doping level is calculated by the use of the well known equation describing the relation between junction depletion layer charge and the applied voltage. If minimum channel length device is used, it may be possible to obtain even higher stimulation voltages. This is due to lateral bridging of the source and drain depletion layers, thus screening the depletion type channel from the substrate.
The use of a floating gate configuration eliminates the sensitivity of the transistor output signal to the exact location of the VSC on the MOS channel, leading to significantly narrower distribution of the signals that have to be detected.
It should be clear that bi-direction signal transfer utilizes the same location on a semiconductor device (a single transistor) for both the stimulation and the sensing. However, two locally adjacent identical transistors can be utilized with the same VSC, one for stimulation and the second for sensing. The use of a depletion type transistor, which is normally-on, enables to eliminate the need for any DC bias between the transistor and the solution containing the VSC. Thus, electrical signal coming from the VSC through the binding moieties induces a gate voltage which affects the surface potential of the active component, thereby increasing or decreasing a current passing the active component between source and drain electrodes. The transistor thereby serving as a sensor. To stimulate the VSC activity, the source is disconnected from its supply, and the neuron stimulation voltage is applied to the drain. As a result, the source, channel and drain will be at the same voltage and through the capacitive coupling to the floating gate and the neuron, will activate the letter. It should be mentioned that the roles of the source and drain can be exchanged in the stimulation process.
The switching of the source and drain during the stimulation process may be performed by utilizing two transistors, each of regular enhancement type, on both sides of the depletion type transistor. These regular type transistors are associated with the source and drain, respectively, of the depletion type transistor.
The neuron sensing and stimulation processes can be achieved in a device including the electrical junction between a floating gate depletion type transistor and a VSC, and an additional switching transistor connected to the gate of the floating gate depletion type transistor. In such a device, the neuron stimulation is carried out by supplying voltage to the gate of the switching transistor.
Thus, according to another aspect of the present invention, there is provided a device for selectively detecting voltage changes from a VSC and transferring voltage changes to the VSC, the device comprising:
an electrical junction between a floating gate depletion type transistor and the VSC, which is associated with the floating gate and is capable of being stimulated by a voltage pulse applied to the gate of the floating gate transistor; and
a switching transistor connected by either one of its source and drain electrodes to the gate of said floating gate transistor to apply said voltage pulse by supplying voltage to a gate of the switching transistor.
The transistor structure is provided with an additional electrostatic screening layer, e.g., gold layer, which covers the entire circuit area except for openings above the floating gates. This enables to reduce noise to such low levels that will enable reliable detection of the neuron signals on one hand and prevent unintended activation of the VSC on the other hand. Furthermore, the existence of the screening which is kept at the potential of the biological solution, further reduces the risk of electrochemical corrosion processes.
The anchoring of the VSC to the external surface of the transistor can be achieved by a plurality of binding moieties such as antibodies, receptors, ligands, lectins and adhesion molecules. Where the VSC is a neuron, typically the biological binding molecules are adhesion molecules such as small molecular weight peptides derived from the neurite promoting domains of laminine (an extracellular matrix) protein) and in particular two well studied synthetic peptides, 8 and 10 amino-acids each having the following sequences:
Lys-Val-Ala-Val-Ser-Ala-Asp-Arg; and
Cys-Ser-Arg-Ala-Arg-Lys-Gin-Ala-Ala-Ser; [PA 22-2 and P20-GCxe2x80x94Ref.6].
Where the VSC is a neuron, the binding moieties may be used not only to anchor the VSC to the surface of the transistor, but also to direct the growth of the neuron to the proper location in the transistor, and repulse its growth from an undesired location. This regulated growth may be achieved by conjugating to the surface of the transistor alternating micro strips of growth promoting molecules such as polylysines, and growth repulsive molecules such as collapsin. These micro strips will ensure that the actin-based motality of the growth will be directed to the desired location on the surface of the transistor.
The voltage transfer between the membrane of the VSC and the external surface of the transmitter may be mediated by hyper-polarizable chromophores. These chromophores are very sensitive to the electrical signals of a nerve cell where such signals cause a charge in the dipole moment and charge density distribution in these chromophores. These changes cause a change in the surface potential of the transistor to which these chromophores are attached.
By a preferred embodiment the electrical junction of the invention features all of the above characteristics, i.e. it enables bi-directional voltage transfer between the VSC and the transistor with no DC bias between the two; the VSC is anchored to the surface of the transistor by biological binding moieties; and the voltage transfer in both direction is mediated by voltage sensitive dye.
By a preferred embodiment the transistor of the junction utilizes silicon-based integrated technology, but may alternatively utilize any other semiconductor structure, e.g. GaAs-based.
By another aspect of the present invention, the invention concerns an array of at least two electrical junctions. Each electrical junction may be designed as described above, namely a single transistor for a single neuron. Alternatively, at least two locally adjacent transistors may be associated with a common neuron, in which case one of the transistors may serve for VSC stimulation, and the other for sensing purposes.
By another aspect, the invention concerns a hybrid electronic device comprising the junction of the invention. The transistor is a depletion type device with a floating gate capacitance coupled to a VSC. A power supply maintains potential difference between source and drain electrodes. By maintaining this potential difference constant, the transistor operates as a sensor for detecting signals coming from the VSC through the current changes caused by this coming signal. By replacing this potential difference by a high voltage applied to the source, channel, and drain of the transistor; it acts as a stimulator of the VSC activity. Preferably, an additional metal layer is used for screening purposes. Selective-sites for the neurons are provided by proper openings in the screening metal layer and by using controlled substrate-neuron linking chemistry.
Thus, the present invention provides an advanced MOS-FET structure, which has larger tolerance for the placement of the VSC over the MOS-FET device by using floating gate devices, eliminates the need for DC bias by using depletion type devices, and reduces the noise level as well as minimize corrosion processes by a screening technique and selective-sites for the neurons, using controlled substrate-neuron linking chemistry.
The device of the invention may also be used to detect voltage changes from a plurality of VSC and/or to transfer voltage changes to a plurality of VSCs and in that case it should comprise the array of the invention wherein each transistor in the array is electrically coupled as described above.
By another embodiment the transistor may have immobilized on its external surface by binding moieties as described above. The transistor may also have immobilized on its surface various growth promoting and growth repulsive molecules, such as those described above in order to regulate the growth of the VSC, and notably the neuron only to regions of the transistor wherein electrical coupling is desired.
Alternatively, or in addition to having immobilized thereon-binding moieties, the transistor of the invention may have immobilized thereon hyper-polarizable chromophores. The attachment is done by chemical reaction on the outer layer of the transistor forming monolayer multi-layers or dendrimers of polarizable chromophores with polar ordering (all the di-poles are pointed either toward or away from the surface).
Since the surface of the VSC is not smooth, the space between said surface and the flat surface of the transistor is irregular. In order to decrease to a minimum the xe2x80x9cshuntxe2x80x9d produced by the electrolyte-containing solution present in that space, it is desired to partially seal that space. Therefore, it is desired to attach either to the hyper-polarizable chromophore, or to the binding moieties on spaces of varying length, or alternatively, produce hyper-polarizable chromophores of varying length so that not withstanding the fact that some regions of the VSC membrane are at different distances from the transistor surface, essentially all these distances are bridged by the spacer and the hyper-polarizable chromophore; spacer and binding moiety; or hyper-polarizable chromophores of varying lengths. Alternatively, the spacers may be used by itself to close the gap, i.e. without any binding moieties of hyper-polarizable chromophores provide a closure of the cleft.
Typically, the length of the spacer should vary from about between 1 nm to 30 nm.
The spacers may be constructed in a xe2x80x9ctree likexe2x80x9d form wherein various xe2x80x9cbranchesxe2x80x9d of the tree are at varying lengths from the surface of the transistor. Alternatively, the spacers or the varying length hyper-polarizable chromophores may be positioned as essentially straight molecules of varying length arranged at a spatial arrangement so that in each region there are a plurality of spacers or hyper-polarizable chromophores of different lengths. Examples of molecules which are suitable to be used as spacers are inert molecules terminated with chemical functionality capable of anchoring polarizable chromophores, e.g. alkylhalide, benzylhalide, acylhalide, amine, active ester, etc., oligosaccharides, straight or branched hydrocarbon molecules, polymers, poly(4-vinylpyridine) and poly (4-chloromethylstyrene).
By a third aspect, the present invention concerns methods for the production of any one of the above transistors.
By one embodiment, the method for the production of a transistor utilizing fabrication of a MOS-FET device in a semiconductor substrate, wherein the external surface of said device is patterned to define selective sites for at least one VSC, said sites being displaced in a horizontal plane with respect to a location of an active component of the device.
By another aspect the present invention concerns an electrochemical junction between a cell which secretes an agent and a transistor. This electro-chemical junction is in fact xe2x80x9cartificial chemical synapsexe2x80x9d wherein the pre-synaptic region is of a live biological secreting cell, while the xe2x80x9cpost synapticxe2x80x9d region is a transistor. The principle of the artificial chemical synapse is that the post synaptic transistor bears on its surface recognition moieties, such as receptors which are capable of binding of the secreted agent. The binding of the agent to the recognition moiety changes at least one electrical property of the transistor which can be measured. Typically, the electrical property is changed di-pole moment of the recognition moiety which changes as a result of the secreted agent. Alternatively, or in addition, the change in electrical property may be a change in capacitance of the molecules pressed on the surface of the transistor.
The electrochemical junction of the invention, also comprises a catalytic moiety, such as an enzyme which can terminate that binding between the secreted agent and its recognition moiety. For example, where the catalytic moiety is an enzyme capable of degradation of the secreted agent, it will quickly eliminate the secreted agents present in the space between the agent secreting cell and the surface of the transmitter, and thus shift the equilibrium of the binding of the agent to its recognition, so that the agents are detached from the recognition moiety and subsequently also degradation. This catalytic activity enables to xe2x80x9cinitializexe2x80x9d or xe2x80x9cregeneratexe2x80x9d the transistor very quickly back to a situation where its recognition moieties are unbound and thus capable of sensing other concentrations of secreted agents. The catalytic moiety in fact enable to monitor essentially xe2x80x9con-linexe2x80x9d fluctuations in the concentration or presence of the secreted agent in the sample.
Thus, the present invention concerns an electrochemical junction between an agent-secreting cell and a transistor comprising:
the agent-secreting region of the cell positioned at an orientation enabling transfer of the agent to a location on the surface of the transistor, said location having immobilized thereon recognition moieties capable of affinity binding to said agents; said binding between the recognition moiety and the agent causing the modulation of at least one electrochemical property of the transistor; said location further comprising catalytic moieties capable of degradation of said agent.
Where the agent secreting cell is a neuron, the secreted agent is a neurotransmitter and the agent secreting region of the cell is a pre-synaptic region of the neuron. The orientation of the agent secreting region in respect to the transistor should be either such which enables transfer due to the fact that the two are adjacent, or alternatively, they may be distanced from each other and the circulation such the blood may bring the secreted agent into the vicinity of the transistor.